Currently, RAT (Radio Access Technology) of W-CDMA (Wideband-Code Division Multiple Access, see Non-patent Document 1) defined by 3GPP (3rd Generation Partnership Project) has been standardized as the third-generation cellular-mobile-communication method, and services thereof have started sequentially. In the W-CDMA system, a compressed mode is defined as a function of monitoring a base station device on a different frequency upon an inter-frequency handover between cells belonging to the same RAT, an inter-RAT handover, and an intra-RAT handover.
FIG. 13 at (a) shows a case where the compressed mode is applied to DPCH (Dedicated Physical Channel) of W-CDMA and monitoring of a base station device on a different frequency is in execution.
The base station device generates a gap that is a transmission intermission as shown in FIG. 13 at (a) and suspends data transmission over the dedicated physical channel at the gap. In FIG. 13 at (a), one frame has a time length of 10 ms, and the gap is generated at a part of a frame. On the other hand, a mobile station device switches a frequency utilizing the gap and monitors the base station device on the different frequency.
In 3GPP, HSDPA (High Speed Downlink Packet Access) that implements high-speed downlink packet transmission of the approximate maximum transmission speed of 14.4 Mbps that is the expansion of the W-CDMA radio interface is standardized. In the downlink, HS-SCCH (High Speed-Downlink Shared Control Channel) and HS-PDSCH (High Speed-Physical Downlink Shared Channel) are additionally defined as independent channels different from the dedicated channel to which the compressed mode is normally applied. In the uplink, HS-DPCCH (High Speed Dedicated Physical Control Channel) is defined additionally.
AMCS (Adaptive Modulation and Coding Scheme) is adopted in HSDPA. The AMCS is a method in which radio transmission parameters, such as the data-modulation multiple-value number of the shared data channel, an error correcting method, an error-correction encoding ratio, the data-modulation multiple-value number, a code spreading factor of time and frequency axes, and the multi-code multiplexed number, are switched according to a downlink CQI (Channel Quality Indication) that is a propagation path condition of each mobile station device to efficiently execute the high-speed packet-data transmission. Additionally, HARQ (Hybrid Automatic Repeat reQuest) is adopted. The mobile station device feeds ACK/NACK (Acknowledgement/Negative Acknowledgement) that is received transmittal confirmation information, and the CQI back to the base station device over the dedicated control channel. The base station device executes scheduling so as not to transmit the HS-PDSCH to a mobile station device in a gap section generated in the compressed mode upon HSDPA (FIG. 13 at (c) explained hereinafter).
FIG. 13 at (b) and (c) shows an example of a packet signal transmitted from the base station device to the mobile station device. FIG. 13 at (b) shows an example of the HS-SCCH transmitted from the base station device to the mobile station device. FIG. 13 at (c) shows an example of the HS-PDSCH transmitted from the base station device to the mobile station device.
The HS-SCCH (FIG. 13 at (b)) is used for indicating whether the packet data transmitted over the HS-PDSCH (FIG. 13 at (c)) is addressed to the mobile station device or another mobile station device.
FIG. 13 at (b) shows that the HS-PDSCH has indicated the packet data addressed to the mobile station device (corresponding to the hatched frames therein). Arrows m1 to m5 indicate to which subframe of the HS-SCCH the packet data to be received by the mobile station device is actually transmitted.
FIG. 14 is a sequence chart showing the processing of the mobile communication system in execution of the compressed mode. The mobile station device reports a message including a measurement result of a serving cell or neighboring cells that is being currently measured to the base station device (step S01). The base station device determines whether or not gap generation is necessary for a handover requiring a different frequency measurement for each mobile station device based on the received measurement result (step S02). The base station device transmits a message including gap pattern information to a mobile station device that is determined to require the gap generation (step S03). The mobile station device receiving the message transmits a response message to the base station device (step S04), executes gap generation control according to the gap pattern, and commences a monitoring of a base station device allocated a different frequency (step S05). The radio communication at steps S01, S03, and S04 between the mobile station device and the base station device are executed by a control signal called an L3 message at L3 (Layer 3) that is an upper network layer.
In HSDPA, a method for the mobile station device to suspend a CQI report over the uplink HS-DPCCH in order to reduce the transmission power and the uplink interference level of the mobile station device in the case of no packet data being addressed to the mobile station device in a given section during packet communication, i.e., while the mobile station device receives no data over the HS-PDSCH, has been proposed (see Non-patent Document 3).
FIG. 15 is a sequence chart showing the processing of the mobile communication system related to the CQI-report suspension. The base station device has a function of monitoring a transmission data buffer. If no transmission data occurs for a given period after the buffer becomes empty, the base station device instructs a CQI-report suspension to the mobile station device (step S11). As a result, the mobile station device suspends the CQI report to the base station device (step S12). The CQI-report suspension is indicated from the base station device to the mobile station device through the HS-SCCH.
If a transmission of data is detected, the base station device immediately instructs a CQI-report resumption to the mobile station device through the HS-SCCH (step S13). As a result, the mobile station device resumes the CQI report to the base station device (step S14). The HS-SCCH is an L1 message that is not transferred to the upper layer and terminated at L1 (Layer 1). The mobile station device decodes signal bits of the HS-SCCH and thereby recognizes the CQI-report suspension or resumption.
On the other hand, there are communication systems called EUTRA (Evolved Universal Terrestrial Radio Access) and EUTRAN (Evolved Universal Terrestrial Radio Access Network) (see Non-patent Document 4). OFDMA (Orthogonal Frequency Division Multiplexing Access) to which the AMCS is applied is proposed as an EUTRA downlink. In addition, a downlink radio-frame configuration and a radio-channel mapping method based on the CQI are proposed (see Non-patent Document 4).
As a gap control method in EUTRA/EUTRAN, similar to FIG. 14, in addition to the method in which the base station device determines gap necessity based on the measurement result of the mobile station device and executes scheduling in consideration of the mobile station device that requires a gap, an autonomous gap control method in which the mobile station device measures an instantaneous CQI, feeds the instantaneous CQI back to the base station device, and thereby autonomously controls gap generation is proposed (see Non-patent Document 5).
A gap in EUTRA/EUTRAN indicates a section in which the base station device executes packet scheduling so as not to allocate data transmission and reception to the mobile station device so that the mobile station device can monitor a base station device on a different frequency, and which is different from a compressed-mode execution section in W-CDMA.
FIG. 16 at (a) and (b) is an explanatory view of the autonomous gap generation control executed by the mobile station device. The mobile station device receives a pilot signal of a common pilot channel from the base station device, measures an instantaneous CQI at a given CQI-measurement interval, and reports the measured instantaneous CQI to the base station device. The instantaneous CQI is instantaneous power of the pilot signal as an example. At the same time, the mobile station device calculates an average CQI by averaging the instantaneous CQIs at a given period. The mobile station device compares the measured average CQI with a CQI threshold of the system parameters. If the average CQI is greater than the CQI threshold, the mobile station device sets a normal mode thereto (see FIG. 16 at (a)). If the average CQI is smaller than the CQI threshold, the mobile station device sets a measurement mode for monitoring a base station device on a different frequency to the mobile station device (see FIG. 16 at (a)). If the measured instantaneous CQI is smaller than the average CQI in the measurement mode, the mobile station device suspends reception or transmission at the frequency utilized by the connected base station device, and generates a gap section. When receiving the report of the instantaneous CQI, the base station device calculates the average CQI of the mobile station device similar to the mobile station device. The calculated average CQI is compared with the CQI threshold of the system parameters. If the average CQI is greater than the CQI threshold, the base station device sets the normal mode thereto. If the average CQI is smaller than the CQI threshold, the base station device sets the measurement mode thereto. If the measured instantaneous CQI is smaller than the average CQI in the measurement mode, the base station device suspends the transmission of packet data addressed to the connected mobile station device, and generates a gap. FIG. 16 at (b) is a partially enlarged view of FIG. 16 at (a) and schematically shows a state where multiple gaps are generated continuously.    Non-patent Document 1: “W-CDMA Mobile Communication System” by Keiji Tachikawa, ISBN 4-621-04894-5    Non-patent Document 2: 3GPP TR (Technical Report) 25.858, and 3GPP HSDPA-specification-related document    Non-patent Document 3: 3GPP TR (Technical Report) 25.903, V0.2.0 (2005-11), Continuous Connectivity for Packet Data Users.    Non-patent Document 4: 3GPP TR (Technical Report) 25.814, V1.1.1 (2006-2), Physical Layer Aspects for Evolved UTRA.    Non-patent Document 5: NTT DoCoMo, Inc. “Measurement for LTE Intra- and Inter-RAT Mobility”, 3GPP TSG RAN WG2 Meeting #50, Sophia Antipolis, France; 9-13 Jan. 2006, R2-060086.